Expansion Vessel For Primary Circuit - Viessmann VITOCAL 300-G Technical Manual

Design information
Brine distributors for two-stage heat pump (BW+BWS) and single
stage heat pump type BW 145
The brine distributors for geothermal probes must be designed and
sized by a specialist contractor (e.g. Viessmann geothermal depart-
ment or an engineering consultancy). The guide values given above
include an additional 20 %.
Example calculations for sizing the heat source
Selection of the heat pump
Building heat load (net heat load)
DHW heating supplement for
a 3-person household
Power-OFF periods
Total heat load of the building
System temperature (at min. outside temp. –14 °C)
Heat pump operating point
The heat pump with a heating output of 6.2 kW (incl. supplement for power-OFF periods, excl. DHW heating), refrigerating capacity
3
= 4.9 kW corresponds to the required output.
²
K
Sizing the geothermal probe as double U-pipe
Average extraction rate ³
= 4.9 kW
²
K
Probe length L = ² /³
K E
Selected pipe for the probe: PE 32 × 3.0 (2.9) with 0.531 l/m
Required amount of heat transfer medium (V
Take the content of the geothermal probe including all supply lines, plus the volume of fittings and the heat pump into consideration.
Provide manifolds when using > 1 probe. Size the supply line larger than the pipe circuits; we recommend PE 32 to PE 63.
■ Geothermal probe as double U-shaped pipe
■ Supply line: 10 m (2 × 5 m) with PE 32 × 3.0 (2.9)
V = 2 × Probe length L × 2 × Pipeline volume + Supply line length × Pipeline volume
R
= 2 × 100 m × 2 × 0.531 l/m + 10 m × 0.531 l/m = 217.7 l
Selected: 220 litre (incl. heat transfer medium in the fittings and the heat pump)
Pressure drop of the geothermal probe
Heat transfer medium: Tyfocor
Flow rate, heat pumps with 6.2 kW: 900 l/h
Flow rate per U-shaped pipe: 900 l/h : 2 = 450 l/h
Δp = R value × pipe length
Δp = 46.9 Pa/m × 2 × 100 m = 9380 Pa
Double U-shaped pipe probe
Δp = 190 Pa/m × 10 m = 1900 Pa
Supply line
Δp = 40000 Pa = 400 mbar (max. ext. pressure drop, primary side)
permissible
Δp + Δp
Double U-shaped pipe probe
Result:
The intended geothermal probe can be used with a heat pump with 6.2 kW rated heating output, since Δp =
Δp + Δp
double U-shaped pipe probe

Expansion vessel for primary circuit

A diaphragm expansion vessel with a capacity of 25 l is sufficient up
to a supply line length of 20 m and up to a size of PE 40.
V = Total system volume (brine) in litres
A
V = Rated volume of the diaphragm expansion vessel in litres
N
V = Increase in volume during system heat-up in litres
Z
= V · β
A
β = Expansion factor (β for Tyfocor = 0.01)
V = Safety hydraulic seal (heat transfer medium Tyfocor) in litres
V
= V × (hydraulic seal: 0.005), at least 3 l (to DIN 4807)
A
VIESMANN
40
(cont.)
= 50 W/m probe length
E
= 4900 W/50 W/m = 98 m ≈ 100 m
)
R
= 9380 Pa + 1900 Pa = 11280 Pa ≙ 112 mbar
supply line
does not exceed the value for Δp
supply line
4.8 kW
0.75 kW (see chapter "DHW heating supplement": 0.75 kW < 20 % of building heat
load)
3 × 2 h/d (only 4 h are taken into consideration, see chapter "Mono-mode opera-
tion")
5.76 kW
45/40 °C
B0/W35
R value (resistance value) for PE 32 × 3.0 (2.9) (see tables Pressure
drop for pipelines):
■ At 450 l/h ≈ 46.9 Pa/m
■ At 900 l/h ≈ 190 Pa/m
.
permissible
Detailed calculations are required for greater lengths.
VITOCAL 300-G